AAV2-RCBTB1 Gene Therapy Prevents Retinal Thinning and Mitochondrial Damage in RCBTB1-Deficient Mice

Biallelic pathogenic variants in the RCC1 and BTB domain-containing protein 1 (RCBTB1) gene are known to cause an adult-onset retinal dystrophy, leading to progressive vision loss. Current therapeutic options for such genetic retinal dystrophies are often limited, highlighting an urgent need for effective interventions. This study explores gene replacement therapy as a promising strategy to restore RCBTB1 function and mitigate the disease progression, particularly focusing on the observed mitochondrial damage and photoreceptor degeneration in affected individuals.

Researchers generated Rcbtb1-knockout (KO) mice by deleting exons 2 and 3 of the Rcbtb1 gene to model the human condition. Wild-type (WT) and Rcbtb1-KO mice were assessed at 3, 8, and 14 months using optical coherence tomography (OCT) and electroretinography (ERG). Retinal ultrastructure was examined via transmission electron microscopy (TEM). At 2 months of age, KO mice received subretinal injections of either AAV2-RCBTB1 vector or a control AAV2-enhanced green fluorescent protein (EGFP) vector. Mice were then analyzed at 8 months post-injection, with retinal gene expression evaluated by quantitative PCR and immunohistochemistry.

Retinal Rcbtb1 expression was completely absent in Rcbtb1-KO mice. By 8 months of age, Rcbtb1-KO mice exhibited significantly reduced outer retinal thickness compared to WT controls. Ultrastructural analysis revealed increased mitochondrial damage within retinal pigment epithelial (RPE) cells and a higher frequency of mitochondria with oxidative inclusions in photoreceptor inner segments in 8-month-old Rcbtb1-KO mice. Degenerating RPE and photoreceptors were also observed, alongside a thicker Bruch's membrane containing druse-like deposits. The most impactful finding was the therapeutic effect of gene therapy:

Treatment with AAV2-RCBTB1 induced sustained RCBTB1 expression and successfully preserved outer retinal thickness in 8-month-old Rcbtb1-KO mice, effectively preventing the progressive retinal thinning observed in untreated KO animals.